1. Field of the Invention
The present invention relates to nonreciprocal circuit devices such as isolators and circulators used at microwave frequencies and communication apparatuses incorporating the same.
2. Description of the Related Art
Conventionally, a lumped-constant circulator is formed by containing a plurality of mutually intersecting central conductors arranged near a ferrite plate and a magnet for applying a DC magnetic field to the ferrite plate in a case. An isolator is formed by arranging a terminating resistor at a predetermined port of three ports included in the circulator.
Specifically, the central conductors are connected to each other at a connecting portion having the same shape as the bottom of the ferrite plate. The ferrite plate is placed on the connecting portion. Three central conductors extended from the connecting portion are bent to enclose the ferrite plate at angles of approximately 120 degrees with respect to each other. This structure constitutes a ferrite assembly. The ferrite assembly is contained together with matching capacitors and the terminating resistor in a resin case. The resin case and the permanent magnet are enclosed by upper and lower box-like yokes formed of a magnetic metal to constitute an isolator.
With the increasingly reduced sizes and weights of the recent mobile communication apparatuses, there has also been a growing demand for the size (including height) and weight reductions of components used in the apparatuses. Nonreciprocal circuit devices are not exceptional. In a conventional nonreciprocal circuit device, components constituting the device are stacked on a mounting surface of a substrate. Thus, in order to reduce the size and height of the entire device, the thickness of the components have been reduced.
For example, when assuming that the thickness of a ferrite plate is 0.3 mm, the thickness of a permanent magnet is 0.5 mm, the thickness of a yoke and a substrate is 0.2 mm, respectively, and the thickness of each central conductor is 0.05 mm, two central conductors intersecting each other on the top and bottom of the ferrite plate, the thickness of the entire device is 1.6 mm, resulting from a simple calculation by an equation 0.3+0.5+0.2xc3x972+0.2+0.05xc3x974=1.6. However, according to the recent market demand, the thickness of the nonreciprocal circuit device has been required to be 1.5 mm or less. In order to meet the market demand, for example, when the thickness of the ferrite plate or the permanent magnet is reduced, a desired static magnetic field intensity cannot be obtained and the electric characteristics of the device is thereby inevitably deteriorated.
Accordingly, it is an object of the present invention to provide a nonreciprocal circuit device capable of reducing the size, height, and weight, while preventing deterioration of the electric characteristics of the device. It is another object of the invention to provide a communication apparatus incorporating the nonreciprocal circuit device.
According to a first aspect of the present invention, there is provided a nonreciprocal circuit device including a plurality of central conductors mutually intersecting in an electrically insulated state, a ferrite assembly including the central conductors and a ferrite member, and at least one magnet arranged for applying a static magnetic field to the ferrite member, in which main surfaces of the ferrite member and the magnet are arranged perpendicularly to a mounting surface of a substrate. With this arrangement, since the thickness direction of each of the components constituting the nonreciprocal circuit device is oriented toward the direction parallel to the mounting surface of the substrate. Thus, without the need for making the components thinner forcefully, the entire nonreciprocal circuit device can be miniaturized reducing its height.
In addition, this nonreciprocal circuit device may further include a yoke composed of planar portions contacted with the external surfaces of a pair of magnets or a pair of a magnet and a magnetic member arranged with the ferrite assembly sandwiched therebetween and another planar portion bridging the planar portions. With this arrangement, a predetermined static magnetic field can be applied to the ferrite member even when the magnets are small. Thus, while preventing deterioration of the electric characteristics of the device, the entire device can be miniaturized.
In addition, in this nonreciprocal circuit device, the bridging planar portion may define substantially a plane. As a result, since the weight of the yoke is reduced, the weight of the entire device can also be reduced and cost reduction can be achieved. In addition, with this arrangement, since the static magnetic field generated by the magnets does not bend, it can be applied perpendicularly to the ferrite member in a manner that the magnetic field is uniformly distributed.
In addition, in the nonreciprocal circuit device at least one hole is provided in the yoke, the hole being formed near the ferrite member. For example, the hole may be provided in the planar portion of the yoke parallel or perpendicular to the mounting substrate, or may be extended from the planar portion parallel to the substrate to the planar portions perpendicular to the substrate. This structure can prevent the static magnetic field generated by the magnets from being bent due to the yoke. Then, the static magnetic field can be applied perpendicularly to the ferrite member in the manner that the magnetic field distribution is uniformly provided.
Furthermore, in this reciprocal circuit device, the opening of the hole may define a substantially quadrangle shape. With this arrangement, the small opening area can more increase the effect of prevention of the bending of the static magnetic field given by the hole.
Furthermore, in the nonreciprocal circuit device, the hole may be formed such that the dimension of a projected planar form of the hole in a direction perpendicular to the main surfaces of the ferrite member includes the gap between the magnets or the gap between the magnet and the magnetic member sandwiching the ferrite assembly, and the dimension of a projected planar form of the hole in a direction parallel to the main surfaces of the ferrite member includes the width of the ferrite member in the direction parallel to the main surfaces. In this arrangement, without making the opening size of the hole larger than necessary, the effect of prevention of the bending of the static magnetic field given by the hole improves.
In addition, in this nonreciprocal circuit device, the yoke may be used as a case and the hole may be covered with a nonmagnetic film. Or, the yoke may be filled with a resin. With this arrangement, the case can be more dust-proof and damp-proof. Moreover, this prevents problems such as open circuitry and short circuit, when performing reflow soldering, the soldered parts of metal wires are melted and the metal wires result in floating.
In addition, the nonreciprocal circuit device may further include a cavity or a hole formed in the planar portion of the yoke which is parallel to the mounting substrate or in the mounting substrate to fit the ferrite assembly or each magnet thereinto. In this arrangement, since the ferrite assembly or the magnets can be easily fixed inside the nonreciprocal circuit device, any special members for fixing the components are not required.
In addition, in this nonreciprocal circuit device, the ferrite member may have a polygonal planar shape with four or more sides. Accordingly, the ferrite assembly can be easily fixed inside the device and also the entire device can be miniaturized reducing the height.
In addition, the central conductors may be metal wires having electrically insulated surfaces, and the ferrite member may be wound with the central conductors to constitute the ferrite assembly. In this arrangement, even when using a compact ferrite member, the inductance of the central conductors can be sufficiently provided.
Furthermore, in this nonreciprocal circuit device, the diameter of each metal wire may be 0.1 mm or less. In this case, without increasing the insertion loss, the nonreciprocal circuit device can be miniaturized.
Furthermore, the central conductors may be metallic foils and the ferrite member may be wound with the central conductors to form the ferrite assembly. In this arrangement, since the ferrite assembly is made thinner, the entire device can be made compact.
Furthermore, this nonreciprocal circuit device may have two central conductors, one end of each conductor being grounded and the other end of the conductors being connected to input/output terminals or components connected to the input/output terminals. In this arrangement, for example, unlike a case in which three central conductors are provided to connect an impedance matching circuit to a third central conductor, no impedance circuit depending on a frequency is arranged. Accordingly, wider band characteristics can be obtained.
In addition, the thickness of the yoke may be 0.2 mm or less. As a result, without reducing vibration resistance strength and fall-shock tolerance strength, the entire device can be miniaturized while reducing the height of the device.
According to a second aspect of the invention, there is provided a communication apparatus including the nonreciprocal circuit device of the invention. For example, the nonreciprocal circuit device is arranged in the output section of a transmission signal amplifying circuit.